1. Field of the Invention
The present invention relates to a head assembly for a chip mounter, and more particularly, to a head assembly for a chip mounter including a nozzle spindle for automatically mounting electronic components such as integrated circuits (ICs), diodes, condensers, and resistors on a printed circuit board (PCB).
2. Description of the Related Art
A chip mounter is one part of a component mounting assembly for mounting components on a PCB. The chip mounter transfers components supplied by a component feeder to a mounting position of a PCB and mounts the components on the PCB.
Typically, the chip mounter includes a component feeder feeding components to be mounted, a conveyor transferring a PCB, and a head assembly with a nozzle spindle sequentially picking-up electronic components from the component feeder and mounting the picked-up electronic components onto the PCB.
Recently, a plurality of columns of nozzle spindles have been installed in a line within a head assembly to increase component mounting efficiency. That is, the plurality of nozzle spindles sequentially or simultaneously pick up a plurality of electronic components, simultaneously transfer the plurality of picked-up electronic components to a conveyor, and sequentially or simultaneously mount the electronic components on a PCB disposed on the conveyor.
FIG. 1 illustrates a head assembly 9 for an electronic component mounting apparatus disclosed in Japanese Laid-open Publication No. 2002-009491. Referring to FIG. 1, the head assembly 9 includes a nozzle unit 12, elevating axis members 30 arranged in two parallel columns, and nozzles 38 that are disposed below the elevating axis members 30 and which pick up the electronic components.
Upper and lower frames 15 and 16 are fixed to the side of a base 11 and nozzle elevating motors 20 are vertically arranged on the upper frame 15.
To raise and lower one of the elevating axis members 30, rotation of a nozzle elevating motor 20 is transferred to an elevating element 25, which converts the rotational motion of the nozzle elevating motor 20 into a vertical motion of the elevating axis members 30. Thus, a plurality of nozzles can be vertically moved independently, which is possible by independently controlling the nozzle elevating motors 20 by a controller (not shown).
As illustrated in FIG. 1, because a separate nozzle elevating motor 20 is needed to vertically move each of the elevating axis members 30, a separate controller should be provided for each motor 20. Furthermore, the plurality of elevating elements 25 correspond to the plurality of elevating axis members 30 in a 1:1 relationship. Because this configuration increases the overall weight of head assembly 9, the component mounting speed decreases and the electrical power required for moving the head assembly 9 increases. Thus, it is extremely difficult to achieve high-speed, high-precision mounting.
As a mechanism for vertically moving each of the elevating axis members 30 becomes complicated, the manufacturing costs and price of the electronic components increase and the head assembly 9 becomes bulky.
As the demand for high speed electronic component mounting apparatus increases, the number of elevating axis members 30 installed within the head assembly 9 increases. Thus, the above-mentioned problems become more severe and the number of nozzles that can be used is limited.
Meanwhile, as disclosed in the Japanese Laid-open Publication No. 2002-009491, a pulley device may be used to rotate the nozzles. Referring to FIGS. 1 and 2, the head assembly 9 has a first line of four nozzles L1 and a second line of four nozzles L2 arranged along one direction and a nozzle rotating motor 50 mounted between the first and second lines of nozzles L1 and L2. Thus, rotation of each nozzle by the nozzle rotating motor 50 is transferred through one of two upper and lower continuously variable belts 51a and 51b provided corresponding to pulleys on an axis rotator 32 so that each line of nozzles can rotate by the nozzle rotating motor 50.
In this case, referring to FIG. 3, the axis rotator 32 includes driving pulley units 33a and idle pulley units 34a and 34b. Type “A”, “B”, “C”, and “D” combinations of the driving pulley and idler pulley allow the of continuously variable belts 51a and 51b to contact the driving pulley unit 33a mounted on each axis of a line of nozzles to be rotated while permitting the axis rotator 32 on the other line of nozzles to be used as a belt guiding idler. The type “A” combination consists of the driving pulley unit 33a and idle pulley 34b with a bearing 34a at upper and lower portions of the axis rotator 32. The type “B” combination consists of the driving pulley unit 33a and the bearing 34a at upper and lower portions of the axis rotator 32. The type “C” combination has the bearing 34a and the driving pulley unit 33a at the upper and lower portions of the axis rotator 32. The type “D” combination has the idler pulleys 34b with the bearings 34a and the driving pulleys unit 33a at upper and lower portions of the axis rotator 32.
However, a conventional electronic component mounting apparatus uses various types of combinations of pulleys to rotate one nozzle. Types of combinations should be changed to rotate another nozzle. This complicates a mechanism for rotating a nozzle and increases time required for mounting components and the overall weight of head assembly.
Furthermore, because the head assembly uses a belt to rotate the nozzle, the belt may backlash. Due to the backlash, the component cannot be accurately positioned for mounting on the PCB since the nozzle cannot rotate to a position optimally set.